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E are prepared to furnish Levy Haemacytometers in which
American made instruments the difficulties of technique are

largely overcome and the danger of destroying the instrument by loosening the distance plates are avoided as the slide and distance plates are of one solid piece. They may be had with either one or two ruled fields on the same plate. The Neubauer ruling only is made for stock but other rulings may be obtained at extra cost. We can also furnish counting plate of other makes but of the same type bearing Thoma Tuerk, Zappert-Ewing, Neubauer Bass and FuchsRosenthal rulings, either single or double fields. All of the above chambers may be bought either with or without the U. S. Bureau of Standards Certificates.

0.100mm
Aboqmm

In addition we can supply the old style single field plates in almost any ruling

E. H. SARGENT AND COMPANY

Importers, Makers and Dealers in Chemicals

and Chemical Apparatus of High Grade Only 125-127 W. Lake Street

CHICAGO, ILL.

AMERICAN MEDICAL MUSEUM JARS

PATENTED

The first rectangular Museum Jar made in America
Far Superior to the Jars formerly made in Germany

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Made of perfectly clear and colorless glass, thoroughly annealed, so that all internal strains are removed.

The comers and edges are thick. The possibility of breakage is therefore reduced to the minimum.

The surfaces, inside and out, are polished planes, so there is no distortion of the object placed within.

The tops of the jars are ground true and the reinforced edge provides a wide surface for tight sealing.

Bottom surface is ground flat so that the jar sets firmly.
The small recess at the top of the jar will hold a glass rod or frame to support the specimen.

Covers are of the same quality of glass, are polished and correspond with the jar and are ground to fit perfectly.

Made in eleven different sizes as adopted by the International Association

of Medical Museums

Write for Prices and Descriptive Circular

DESIGNED, PATENTED AND DISTRIBUTED BY

Scientific Materials Company

Everything for the Laboratory"
PITTSBURGH, PA.

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For the first time since the announcement of this Balance in September, 1913, we are in position to make immediate shipment from stock on hand, as the production of the Troemner factory has been heretofore continuously oversold. This is made possible by our release from large Government contracts for these Balances.

This Balance was particularly designed to meet the requirements of industrial chemists, and its rigid and robust construction has been found to stand the wear and tear in a works laboratory in a remarkable manner. Sensitivity 1/10th milligram, capacity 200 grams in each pan. With beam graduated on both sides, in mahogany case with glass sides and door, with black, polished plate glass base inside of case. Price.

$75.00 Price subject to change without notice

WHOLESALE AND EXPORT DISTRIBUTORS
ARTHUR H. THOMAS COMPANY

IMPORTERS - DEALERS-EXPORTERS
LABORATORY APPARATUS AND REAGENTS
WEST WASHINGTON SQUARE

PHILADELPHIA, U. S. A.

SCIENCE

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THE AIRPLANE IN SURVEYING AND

MAPPING The airplane, while not a product of the war, owes its present prominent place to the war, and but for the war its development would have been retarded many years. It had few practical uses from the time the Wright brothers first flew their machine at Fort Myer, Va., in 1909 until 1914. It was a plaything to amuse the holiday crowd.

The war changed this situation. The allies and the central powers almost immediately saw the great importance of the airplane in battle and the best brains and energy of the warring nations were given to the problem of making the airplane perform what a few years ago would have been considered miraculous things.

War planes were made for various purposes, which I need not enumerate. But the most important thing done from the airplane was photographing the enemies' lines to obtain many kinds of military information, such as positions of batteries and ammunition dumps, changes in trench systems, troop movements, etc.

The same methods, with some modifications, are now being considered in connection with the mapping of extensive areas by various organizations of this country. In fact, some work has already been done and experiments are being carried on which promise excellent results.

There is so much misinformation regarding surveys and maps, that it seems appropriate for me, as the head of the oldest map-making bureau of the government, to present the mapping situation to this congress, both for your information and as a matter of record.

Surveying and mapping have long histories and the development of the methods now employed took centuries. But the method of airplane surveying has developed like a mush

To what extent is it applicable to our needs? This I shall endeavor to show.

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TYPES OF MAPS

In collecting data for a map those survey- tures in the area to be surveyed. The usual ing methods must be adopted in any particu- method of making such a map is by compass lar case that suit the requirements.

and chain, transit and tape, transit and stadia, should wish only a route map running from or by the plane table. These methods are all one village to another, it would be perfectly very closely allied and such accuracy as may satisfactory to use a compass for direction and be demanded may be obtained by varying the the pacing of a horse or the readings of an

methods used. odometer on a wheel for the distance between the two points. But maps are usually not so

MAPS CONTROLLED BY FIXED POINTS simple as that.

In any event there must be within the area to be surveyed, if it is a large one, a number

of control stations. These control stations There are several types of high grade maps consist of triangulation stations placed on the needed in this country. One must be made highest parts of the ground or traverse staalong the coasts to show the location of the tions along the roads, accurately located in actual shore line and the character of the latitude and longitude and accurately and subground immediately back of the coast in order stantially marked with concrete or rock in that the navigator may be able to locate him- order that they may be recovered and identi. self from topographic features along the shore, fied by the surveyors or engineers who may should he be driven off his course during a wish to see them. storm. In addition the depths of the water There are now many thousands of such staand all obstructions to navigation must be tions in the United States, established prinindicated on this map or chart, and the eleva- cipally by the Coast and Geodetic Survey, tion and shape of the ground on islands and available for the fundamental control of surnear the shore line must be shown by contours. veys and maps. From these stations control

A second class consists of maps on which of the same or of a lower grade of accuracy the features other than elevations are shown may be extended in any direction for the imin their correct horizontal positions. This mediate control of topographic maps. type of map would be practically the same as the third type where the area covered is very OVERLAPS, GAPS AND OFFSETS TO BE AVOIDED level like the coastal plain of Louisiana.

It is readily seen that without the fundaThe third class covers maps of the interior mental control, which extends over the whole or of large islands on which all features, cul- area of the United States, there would be tural and natural, are located in their proper great confusion.

If the control in any one horizontal positions and contours are shown to state is not properly coordinated and corregive the elevations of the ground and the shape lated with that of any other state near it, the of the hills, ridges, valleys, etc.

result will be that when different topographic would be used by engineers in laying out rail- surveys and maps are joined there will be roads and highways, and in conducting vari

overlaps, gaps and offsets which cause no end ous classes of engineering work.

of trouble and confusion to the cartographer These three classes of maps are the ones in and map maker. When there is a single syswhich we are most directly interested.

tem of control for the whole country we avoid The map which shows the horizontal posi- this unfortunate condition. tions of cultural and natural features on the surface of the earth, but no contours, can be 3,000,000 SQUARE MILES, LESS THAN ONE HALF made more rapidly than the one which re

MAPPED quires contouring. All that is needed in the There is to-day only about 40 per cent. of former case is some method of obtaining the the 3,000,000 square miles of the United States direction and distance between each two fea- mapped both as to horizontal positions of the

This map

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